1. Field of the Invention
The present invention relates to a variable valve mechanism, and more particularly to an internal combustion engine's variable valve mechanism that is capable of changing the operating angle and/or lift amount of a valve disc, which opens/closes in synchronism with camshaft rotation.
2. Background Art
The variable valve mechanism disclosed, for instance, by Japanese Patent Laid-open No. 2003-239712 includes a mechanism that is positioned between a cam and a valve disc to change the operating angle and lift amount of the valve disc. This variable valve mechanism has an oscillation arm, which oscillates in synchronism with cam operation, and a rocker arm, which is provided with an arm roller that comes into contact with the oscillation arm. One end of the rocker arm is in contact with the end of a valve stem, and the other end is supported by a lash adjuster. The rocker arm is configured so as to turn in coordination with an oscillation arm's oscillation operation while using a rocker arm end, which is supported by the lash adjuster, as a fulcrum. This variable valve mechanism also includes an adjustment mechanism that changes an oscillation arm's reference arm rotation angle in accordance with a change in the rotation position of a control shaft.
When the reference arm rotation angle of the oscillation arm changes in accordance with a change in the control shaft rotation position, the point of contact between the oscillation arm and arm roller in the above conventional variable valve mechanism changes. When the point of contact changes, a change occurs in the timing with which the rocker arm depresses the valve disc in accordance with a cam operation and in the amount of valve disc depression. Therefore, the above conventional variable valve mechanism can continuously change the operating angle and lift amount of the valve disc by controlling the control shaft rotation position.
Including the above-mentioned document, the applicant is aware of the following documents as a related art of the present invention.
[Patent Document 1]
Japanese Patent Laid-open No. 2003-239712
[Patent Document 2]
Japanese Patent Laid-open No. Hei 7-293216
[Patent Document 3]
Japanese Patent Laid-open No. Hei 7-63023
However, when the lash adjuster, which is positioned at the fulcrum of the rocker arm of the above conventional mechanism, expands/contracts, the fulcrum of the rocker arm moves in the direction of expansion/contraction. Consequently, the point of contact between the oscillation arm and arm roller may change. If the point of contact changes, a change occurs, as described earlier, in the timing with which the rocker arm depresses the valve disc in accordance with a cam operation and in the amount of valve disc depression. In other words, when the lash adjuster expands/contracts to provide zero tappet clearance, an unexpected change may occur in the operating angle and lift amount of the valve disc.